1. Field of the Invention
The present invention relates to a vehicle position detecting apparatus which is used in a map matching apparatus of a navigation apparatus to be mounted on a vehicle.
2. Description of the Related Art
A navigation apparatus calculates routes traveled by a mobile body, such as automobile or the like, and displays the present position, where the vehicle is running, on a map scene which is displayed on a displaying apparatus, thus assisting drivers. The present position of the vehicle is measured by, for example, a GPS (Global Positioning System). Also, the present position may be obtained with the use of the running distance of the vehicle which is measured in accordance with an output from the vehicle speed sensor and a relative bearing of the vehicle which is measured by a gyrocompass. The bearing indicates a direction along a direction in which the vehicle progresses at the time the vehicle has passed the present position.
The present position of the vehicle, obtained in this manner, is often deviated from the present position of the actual vehicle. The measuring error becomes larger as the position of each positioning satellite becomes closer. Apparently, this is due to the fact that the GPS effects triangular surveying with the use of a plurality of positioning satellites. Also, the measuring errors become larger even when the number of the positioning satellites which are used in the measuring is small. The measuring errors are caused because of slipping, or the like, of wheels since the running distance is obtained from the revolution number of the wheels during the measuring of the running distance with the use of the vehicle speed sensor. Also, the gyrocompass causes errors in the bearing measured since the gyrocompass changes, as time passes, due to temperature changes in characteristics of offset, or the like, of output signals.
Also, in an apparatus for measuring the present position of the vehicle with the gyrocompass and the vehicle speed sensor combined, the present position is successively estimated as a position which is reached by the vehicle after running only the newest running distance in the newest bearing measured from the present position in the past. Therefore, the present positions measured subsequently are also deviated successively when the present position in the past is deviated from the actual present position by correction.
In this manner, measured errors are included in the measured present position of the vehicle. Therefore, the navigation apparatus, provided with a map matching apparatus, effects a match processing operation for correcting the present position of the vehicle. The navigation apparatus visually displays the present position on the map scene to effect navigation. The prior art concerning the pattern matching is disclosed in, for example, Japanese Unexamined Patent Publication JP-A 64-41997 (1989).
In the match processing, the running tracks of the vehicle, which is the shape of the running route, is compared with the road shape to correct the present position of the vehicle on the road when the running tracks are similar to the road shape. Namely, assume that the vehicle is running on the road shown on the map scene to correct the position of the vehicle. A plurality of roads sometimes exist near the measured present position in the match processing. At this time, the matching apparatus divides roads into portions called links which are a plurality of linear road portions with corners, intersection points, and both ends, etc., and obtains the similarity degree with respect to each road portion to set the correction portion of the present position on the road portion having the largest degree of similarity. The similarity degree is obtained, based on a difference in bearing between the road of the links and the vehicle, and the distance between the link and the measured present position of the vehicle. The similarity degree becomes larger as the difference in bearing becomes smaller. The similarity degree becomes larger as the distance is shorter.
The running distance of the vehicle from the intersection point approaching position to the intersection point passing position is different in accordance with the positions in the width direction of the road at the approaching and passing time when the vehicle turns to the right and to the left at the intersection point. The data of the road of the map scene are simplified and displayed only as segments showing the length of the road and the direction capable of running. Therefore, it is difficult to calculate the deviation of the running distance from the road data. Also, the grade of the road is not taken into consideration because the map scene is displayed as a plan view seen from the sky. The grade may be different and the length of the actual road may be different when two roads are represented as roads of the same length on the map scene. Further, curved roads may be deformed in digital data. Mountain roads especially become larger in precision error due to a simplification of the road data of the map scene because the road grades are large and there are many curves. The gap of the present position may be sometimes larger conversely when the map match processing is effected in accordance with such map scenes.
Also, in order to reduce the data amount, in the road data of the navigation apparatus roads which have a small amount of traffic and have a smaller use possibility are not included with such trunk roads recorded as data such as those having a heavy in traffic amount in expressways, national roads or the like. In the roads older in the date, the roads newly opened may be not recorded as road.
The map match processing is sometimes effected in accordance with road data having unknown roads not recorded as described above. The navigation apparatus does not correct the present position when the similarity degree calculated with respect to the links are smaller than the predetermined values. Namely, the dead reckoning navigation is used in the navigation without correcting the measured present position, as it is, when the present position of the vehicle and the road are largely separated.
The measured present position, when the vehicle is running on the unknown road, is considered to be separated from any of the many roads recorded. In such a case, the navigation apparatus carries out the dead reckoning navigation, but does not correct the present position. The unknown roads are connected with recorded roads at intersection points. Also, one portion thereof sometimes approaches to the recorded road even when the road is not connected with the recorded road. When the unknown road approaches to the road recorded, the present position of the vehicle existing on the unknown road approaches to the recorded road to increase the similarity degree. At this time, the navigation apparatus of the conventional art corrects the present position onto the recorded road despite the vehicle running on the unknown road. Thus, the navigation apparatus of the conventional art corrects the present position so that the vehicle is deviated from the actual present position and progress bearing conversely to increase errors.
Japanese Unexamined Patent Publication JP-A 3-265887(1991) discloses the art of processing the map match processing with respect to the road on which the actual vehicle is running when the road is branched at a shallow angle at an intersection point. The navigation apparatus of the present publication sets correcting candidate points to be corrected in the position of the vehicle respectively on two roads branched when the road is branched to calculate evaluation values with respect to the respective correcting candidate points. The evaluation values are determined from the present position of the vehicle and the agreement degree between the progress bearing and the road direction. The evaluation with respect to each road is continued from the production of the correcting candidate points at the intersection point to the continuous reduction where the evaluation value with respect to the correcting candidate points becomes equal to or less than a predetermined value. Therefore, the evaluation is effected in parallel with respect to a plurality of roads.
Also, the match processing using the similarity degree sometimes sets the corrected present position onto the road different from the road on which the vehicle is actually running when the difference between the road shape and the running track is large. The running track is sometimes corrected, as if the vehicle makes a U-turn from halfway in the corner to run reversibly in spite of the vehicle running to pass the corner when the difference of the road shape and the running track are large, when the vehicle is running the corner which is bent like the hairpin shape.
FIG. 17A is a diagram showing a running track 2 measured when the vehicle runs on a road 1. The road 1 has a road shape curved into a hairpin bend with links 4 through 7 sequentially connected. The vehicle runs as if it sequentially passes the links 4 through 7 on the road 1. The running track 2 measured at this time is formed by sequentially connecting the present position of the vehicle measured for every predetermined period, and a track portion 9 through 13 which is obtained from the progress bearing measured in the present position.
At this time, a connecting point 15 between the track portions 10 and 11 as one of the measured present positions of the vehicle exists at an almost equal distance to the links 4, 7. In the difference in bearing between the track portion 11 directed at a bearing equal to the progress bearing at the connecting point 15, the difference in bearing with respect to the link 4 is smaller than the difference in bearing with respect to the link 7. Therefore, the similarity degree of the link 4 is smaller as compared with the similarity degree with respect to the link 7. At this time, the matching apparatus corrects the present position corresponding to the connecting point 15, judging that the vehicle is running on the link 4, to shift-move the tracking portions 11 through 13. A connecting point 15a, and tracking portions 11a through 13a of FIG. 17B show the track portions after the correction thereof. A running track 2a, after the correction thereof shown in FIG. 17B, shows such movement as U-turning halfway the corner of the road 1 to run reversibly.
By correcting the present position of the vehicle, match-processing with only the similarity degree with respect to the link as a judging reference in this manner, and the deviation between the actual present position and the present position the navigation apparatus recognizes becomes larger when the road shape is bent like a hairpin bend having a large difference between the road shape and the running track.
The road data are simplified and displayed as segments showing only the length of the roads and the directions capable of running. Although the running distance of the vehicle from the approaching position of the intersection point to the passing position of the intersection point is different in accordance with the positions in the width direction of the road at approaching and passing time when the vehicle turns to left and to right at the intersection point, it is difficult to calculate the difference of the running distance from the road data. Also, the grade of the road is not taken into consideration, because the map scene are displayed as a plan view seen from the sky. Therefore, even if a road is the same as another road in length on the map scene, the roads may be different in actual length because of different grades. Mountain roads especially become larger in the precision errors due to the simplification, because the road data are often simplified due to an extensive number of the links. Effect a map match processing operation based on the road data, and the deviation of the present position sometimes becomes larger conversely.
The navigation apparatus effects its navigation with the corrected present vehicle positions being displayed on the map scene. The actual present position of the vehicle is different from the present position displayed when the running track is U-turned to run reversibly by the match processing although the vehicle is not actually U-turned, as described above. Therefore, different feelings are given to the user of the navigation apparatus such as, for example, a driver of the vehicle. Also, an apparatus for measuring the present position of the vehicle with the gyrocompass and the vehicle speed sensor combined estimates of the present position successively as the position where the vehicle has run only by the newest running distance towards the newest progress bearing measured from the past present position. Therefore, when the present position in the past is deviated from the actual present position by correction, as a consequence, the present positions to be measured subsequently are also sequentially deviated.
Japanese Unexamined Patent Publication JP-A 1-276015(1989) discloses a navigation apparatus for vehicle mounting use for estimating and displaying the present position of the vehicle and correcting them by match processing. The navigation apparatus of this prior art obtains the present positions of the vehicle from the progress bearing measured with geomagnetism sensors and the running distance measured with distance sensors. Nodes only are selected, with nodes being on the downstream side of the progress bearing of the vehicle seen from the present position, from among the nodes which are points on the road existing on the predetermined distance from the present position. These selected nodes on the downstream side of the progress bearing are match-processed as the objects of the correction position of the present position.
As described above, the similarity degree is obtained on the basis of the difference in bearing between the link and the vehicle, and the distance between the road and the measured present position of the vehicle. The similarity degree becomes larger as the difference in bearing is smaller. The similarity degree becomes larger as the distance is shorter. Suppose that the vehicle runs in the order of links A1, A2, A3 on a road 21 which is a Y-shaped road branched in such a shallow angle as shown in FIG. 18A. The difference in road bearing between the links A2 and A4 immediately after the branching is small. FIG. 18B is a graph showing time changes in accumulation similarity degree which is the accumulation adding result of the similarity degree with respect to the links A2, A3 and links A4, A5 in the running on the road 21 after branching. A linear line 23 shows time changes in the accumulation similarity degree with respect to the links A2, A3. A linear line 24 shows time changes in accumulation similarity degree with respect to the links A4, A5.
At a time t1 immediately after the vehicle has passed a branch point p, the present position is measured to correct on the road 1 the present position measured. Assume that the present position is corrected respectively into correction points pa1, pb1. The vehicle sometimes becomes larger in similarity degree with respect to the link A4 than in similarity degree with respect to the link A2, in spite of the vehicle running on the link A2, by the measured errors of the present position.
The present position is measured at times t2, t3, t4 continuously. Suppose that the vehicle runs at each link A2, A3, A4, A5 respectively, and similarity degrees are calculated and added accumulatively in parallel. The present position is corrected respectively into corrected points pa2, pb2: pa3, pb3 at times t2, t3 and the accumulation similarity degree is added at almost the same time. A corrected point pb4 is removed from the links A4, A5 so that similarity degree becomes extremely small, because the vehicle actually runs on the links A2, A3 at times t2, t3. The similarity degree with respect to the link A3 has the same degree in size as that obtained at the time t3. Thus, the accumulation similarity degree is reversed in size. It is judged that a possibility of the vehicle running is higher in the links A2, A3 than in the links A4, A5. A link on which the vehicle is running is likely to be taken in a wrong way on a road branched at a shallow angle due to the judgment that the vehicle is running in accordance with the separation degree only immediately after the branching as described above.
Such a navigation apparatus as described above cannot evaluate with respect to unknown roads although the evaluation can be effected on roads which the navigation apparatus itself records. Therefore, it is difficult to evaluate unknown roads and recorded roads in parallel when the vehicle is running on the unknown road. It is difficult to prevent the errors from being increased.
Also, such a navigation apparatus as described above can prevent movements such as U-turning into a reverse running in running track with match processing when the vehicle is running only in a one way direction. The present position cannot be corrected into nodes of the road the vehicle reverses to when the vehicle makes a U-turn and reverses, because the apparatus does not add into the correction object of the present position the nodes on the upstream side of the progress bearing of the vehicle.
Further, such a navigation apparatus as described above can reduce the errors on the branched road. Namely, the errors of the present position in a direction orthogonal to the running direction of the vehicle are corrected. The navigation apparatus effects parallel evaluations with respect to the road only when the road has been branched to reduce the errors of the evaluation value. Therefore, it is difficult to reduce the errors, because the frequency of effecting parallel evaluations is sharply reduced on the roads containing fewer branching such as expressways and so on.
Also, the present position measured by the navigation apparatus makes errors not only in a direction parallel to the running direction of the vehicle, but also in a direction along the running direction of the vehicle. The errors are caused when the running distance measured in the slipping of the vehicle has been deviated as the actual running distance in, for example, the measuring of the present position of the vehicle. Such errors are often caused on gravel roads, snow-covered roads, and so on, where wheels are likely to slip. The present position asked for is set, and deviated in the longitudinal direction along the progress direction of the vehicle from the actual present position in the deviation between the measured running distance and the actual running distance when the present position is obtained in accordance with the running distance and the turning amount.
Also, the errors described above are caused due to simplification into data in the road data which are used in the match processing. To reduce the data amount to be recorded in the navigation apparatus, the roads are simplified and displayed with the length of the road and the direction capable of running as segments. When the vehicle turns to the right or to the left in the crossing point, the running distance of the vehicle from the intersection point approaching position to the intersection point passing position is different by the running track of the vehicle from the intersection point approaching time to the passing time. Especially on the wider roads, the difference results in the manner of passing the positions in the width direction of the road at the intersection point approaching time and passing time.
When the present position is obtained on the basis of the running distance and the turning amount, the obtained present position is deviated in the longitudinal direction from the actual present position when the running distance obtained from the above described road data is deviated from the actual running distance in the present position obtained in accordance with the running distance and the turning amount. It is difficult to obtain such running distance deviation from the simplified road data.
Also, the road data are displayed as a plan view seen from the sky and are simplified in small grade and turning of the road. Accordingly, the length of the actual road may be different from the length of the road in terms of the road data. The precision errors of the road data becomes larger, because the road grades are larger on mountain roads. The running distance to run in terms of the road data is different from the actual running distance measured, thus causing the deviation of the present position determined in terms of the road data.